This invention generally relates to sootblowers and particularly relates to improvements in the frame structure and drive mechanism of a retractable sootblower.
Sootblowers are used to project a stream of blowing medium, such as water, air or steam, against heat transfer surfaces within large scale boilers or other heat exchangers to cause slag and ash encrustations to be removed. The impact of the blowing medium produces mechanical and thermal shock which causes the adhering encrustation layers to be removed.
One general category of sootblowers is known as the long retracting type. These devices have a retractable lance tube which is periodically advanced into and withdrawn from the boiler and which is simultaneously rotated such that one or more nozzles at the end of the lance tube project jets of blowing medium against the encrusted surfaces in the boiler.
Sootblower designers are constantly striving to enhance design efficiency in terms of construction cost, operation, inventory cost and maintenance. In a conventional retractable sootblower, an elongated frame or beam houses a moveable carriage. The carriage drives a lance tube from one end of the frame to the other during the extension and retraction motion. Various configurations for sootblower frames are known.
In one well-known configuration, sheet metal plate stock is press brake formed to define three sides of a generally rectangular shaped member defining the elongated frame. In a typical installation, the open portion of the frame faces downward. The carriage is driven to move within the frame and the frame supports the lance tube suspended therein. Such conventional sootblower frames are known as closed frames since their upper surface is enclosed and inaccessible. Examples of presently known sootblower designs are provided with reference to U.S. Pat. Nos. 2,668,978; 3,439,376; 3,585,673; 3,604,050, 4,229,854 and 4,351,082. Although these closed frame type sootblowers perform in a satisfactory manner, they do have certain drawbacks.
One drawback results from the method in which the frame is formed. Since the three sided frame member is brake formed from flat sheet metal stock, a limitation on the length (typically twenty feet) of the member is presented by the brake forming machine. To form a longer frame member, separate three sided members are butt welded together. Obviously, forming the butt welds requires an additional and separate bonding step to be included in the production operation. Additionally, the presence of the weld is a site for corrosion development.
In certain sootblower applications, it is difficult to service the various mechanisms of the unit through the open bottom portion of the above mentioned closed frame. In these applications, a frame having an open upper portion which would allow the carriage, feed tube, lance tube and drive or gear rack to be removed by withdrawing them up through the top portion of the sootblower frame would be more desirable. Although such open top sootblowers can be produced, when using conventional constructions, specifically designed units would have to be produced for specific installation sites.
Another problem associated with previous types of sootblower frames is the manner in which they are supported at the installation site or plant. Typically, brackets are welded at the installation site onto the sidewalls of the frame at a distance, approximately three to four feet, from the rear bulkhead. The frame is then field welded to various support structures of the plant itself. As a result, the entire weight of the sootblower is being supported by the sidewalls of the beam or frame. This includes not only the weight of the lance tube, the carriage and the beam, but also the weight of the supply piping extending from the poppet valve, sometimes eighty feet below the location of the sootblower assembly itself. The net effect of the piping loads, the carriage weight, the lance tube weight and the other forces generated during cleaning is that the sidewalls of the frame may undergo deflection and develop a permanent set thereby negatively affecting the performance of the sootblower.
Yet another problem associated with sootblowers is that as steam flows through the lance tube, high temperatures are generated within the carriage housing. These temperatures can cause a decrease in life of lubricants. Often, the lubricant which is used to lubricate the bearings supporting the lance hub is also the lubricant used to lubricate the various gears of the carriage's transmission which provides translational and rotational movement of the lance tube. The heat generated within the lance hub thus affects all of the lubricant utilized by the sootblower. In such a carriage housing, significant attention needs to be paid to the condition of the lubricant to ensure that it is in good condition and that serous damage does not occur to the carriage transmission or bearings supporting the lance hub.
With the above limitations in mind, it is an object of this invention to provide a sootblower having a frame which features an open construction and enables the sootblower components to be readily serviced or withdrawn through the bottom or the top of the unit.
Another object of this invention is to provide a frame for a sootblower which can be constructed to any desired length while using a common inventory stock for all lengths. It is also an object to provide a sootblower frame in which the side panels are seamless and formed with a unitary construction.
Still another object of the invention is to provide a sootblower frame which is resistant to corrosion and which is easily inspected for corrosion damage.
Yet another object of the present invention is to provide a sootblower frame which is less susceptible to damage resulting from deflection of the frame under the weight and forces, including piping loads, associated with operation of the sootblower. A related object is to provide and support a frame which is capable of handling an increase in piping weight.
Another primary object of this invention is to decrease the frequency between required servicing of the lubricant used in the sootblower. In particular, the present invention thermally isolates the lubricant used in connection with the various carriage transmission components from the heat transmitted through the lance hub and from the lubricant associated with the lance hub. By doing this, the useful life of the transmission lubricant, as well as the various transmission components themselves, is prolonged. In further achieving the above mentioned object, the present invention also has as one of its objects providing a sootblower in which the lance hub is retained in what may be referred to as a non-lubricated or permanently lubricated fashion. As used herein, these terms are intended to include mountings which eliminate the need to service the lubricant typically required with the prior art.
The various boiler configurations require retractable sootblowers of varying lengths. Such lengths range from only several feet long to ones well in excess of sixty feet. With conventional sootblower designs, the vast difference in size requirements has restricted the use of a common construction component for all the varying lengths of possible sootblower applications. This increases a manufacturer's inventory requirements and adversely affects component costs.
The use of common components for various lengths of sootblowers becomes difficult since significantly different loads will act on the frame structure as a function of its length. For example, as the extended length of the lance tube increases, the loads applied to the frame changes. In addition, significant loads, from both gravity and fluid reaction forces, act on the sootblower lance tube as the sootblower performs its cleaning function. These loads are transferred to the sootblower carriage which is restrained by the frame.
Various designs for an open-type sootblower frame have been proposed. However, such devices are typically costly to manufacture and do not offer a high degree of accessibility since they are generally constructed to provide either top access or bottom access, but not both. Additionally, in an effort to achieve the necessary structural rigidity, closed box sections or tubes have been proposed which are welded to side panels to form ribs bridging the side panels. These closed tubes have also been used to define the side panels themselves. Although the closed tubes would provide adequate structural integrity, they too are available only in certain lengths and require butt welds or cutting to achieve the appropriate lengths. This again involves extra costs and waste. Moreover, closed box tubes are disadvantageous in that they cannot readily be inspected or protected from corrosion. Also, in order to keep their weight at an acceptable level, the metal thickness of the box tube sections must be kept relatively thin. This further degrades corrosion protection.
The sootblower frame in accordance with this invention is readily adapted for different lengths of sootblowers by using various lengths of flat sheet metal for the side panels of the frame. With the shorter sootblower lengths (up to approximately twenty-two feet) the sheet metal side panels can be used without further structural reinforcement. For intermediate lengths, angle iron is welded or bolted along the length of the side panels of the frame to increase its structural integrity and enable it to handle the loads associated with the longer length lance tube. The longest length devices, those generally having a length greater than twenty-two feet to thirty-four feet, require further reinforcing by adding an additional strengthening member to the side panels of the frame.
As mentioned previously, the requirements of joining separate lengths of stock material together to form a sootblower frame of a desired length has its disadvantages. In accordance with this invention, a sootblower frame is provided in which the side panels can be formed from coiled sheet metal stock, available in substantially any length required. Since the side panels do not require forming of any type, with the exception of a flattening or straightening operation, length constraints are virtually eliminated and the side panels can be formed without seams thereby eliminating an inherent weakness of the prior designs.
In some prior sootblowers, a pair of laterally separated guide tracks or rails are provided to suspending the carriage as it moves between its advanced and retracted positions. Frequently, the lance tube is designed to be positioned off-center with respect to the two guide rails. This is known as handedness, left-handedness or right-handedness depending to which side of the lance tube is off-set.
Due to the significant fluid force of the blowing medium acting on the cross-section of the feed tube, substantial pressure forces also act on the carriage and the frame. When handedness is designed into the sootblower, significant imbalances in the forces applied are present. This leads to increased and uneven structural loading on both the frame and carriage.
In one embodiment of the present invention, the sootblower features a balanced orientation with the lance tube being equidistantly positioned between the side tracks thus equalizing the loading of the frame.
The sootblower of the present invention also incorporates an integral rear support as opposed to those prior sootblowers having field welded support brackets on their sidewalls. The rear support of the present invention is provided as an extension of the rear bulkhead. This results in the sidewalls being less stressed and being less likely to deflect or deform. It also enables the sootblower to support increased piping loads without negatively affecting the poppet valve or feed tube designs.
Yet another feature of the present invention is the isolation of the lance hub from the remainder of the carriage assembly and particularly the incorporation of a "dry" lance hub bearing into the sootblower. By isolating the lance hub from the remainder of the carriage assembly, the heat generated by the steam passing through the lance hub is prevented from significantly heating the lubricant of the carriage assembly. The design of the present invention enhances the convective dissipation of heat from the exterior of the lance hub to the surrounding area. The hub itself is rotationally supported in pillow blocks by permanently lubricated specially designed bushings having a high temperature resistance. In addition to requiring no additional lubrication, the bushings allow the lance tube to rotate while constraining thrust loads induced by the steam or blowing medium flowing through the lance tube. Thus, combining the bushings with the enhanced convective cooling allows the lance hub to be rotationally supported without needing an additionally or externally applied lubricant at the bushings.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the preferred embodiments and the appended claims, taken in conjunction with the accompanying drawings.